1. Field of the Invention
The present invention relates to providing span powering to a low power DS3 device or any of a family of SONET multiplexing and/or interface devices that transport electrical signals and optical signals, and/or convert between optical and electrical signals or one type of optical signal (such as OC48) to another (such as Gigabit Ethernet). In particular, the present invention relates to an apparatus for providing span powering to a remotely-located DS3 signal device or other signal device over twisted pair conductors.
2. Description of Related Art
As the demand for high bandwidth, high bit rate communications increases (e.g., to accommodate multimedia applications, in particular), fiber optics technology is rapidly advancing to supply the capacity. Synchronous Optical Network (SONET) is the communication hierarchy that has been specified by the American National Standards Institute (ANSI) as a standard for a high-speed digital hierarchy for optical fiber. SONET defines optical carrier (OC) levels and electrically equivalent synchronous transport signals (STSs) for the fiber-optic based transmission hierarchy. The SONET standard is described in more detail in ANS T1.105 and T1.106, and in Bellcore Telecordia Generic Requirements GR-253-CORE and GR-499 standards, which are incorporated herein by reference. Equipment manufacturers may choose to incorporate a subset of these standards sufficient to permit interoperability of equipment and signals at a basic level, such as the ability to transport a DS3 signal from one OC3 system to a different OC3 system over fiber optic cable.
Before SONET, fiber optic systems in the public telephone network used proprietary architectures, equipment, line codes, multiplexing formats and maintenance procedures. The users of this equipment (e.g., Regional Bell Operating Companies and inter-exchange carriers (IXCs) in the United States, Canada, Korea, and Taiwan, among other countries) desired standards such as SONET so they could employ equipment from different suppliers without experiencing incompatibility problems.
SONET defines a technology for carrying many signals of different capacities through a synchronous, flexible, optical hierarchy using a byte-interleaved multiplexing scheme to simplify multiplexing and provide end-to-end network management. The base signal in SONET is a Synchronous Transport Signal level-1 (STS-1) which operates at 51.84 Megabits per second (Mbps). Higher-level SONET signals are summarized in the following table:
TABLE 1SONET HierarchySignalBit RateCapacitySTS-1, OC-151.840Mb/s28 DS1s or 1 DS3STS-3, OC-3155.520Mb/s84 DS1s or 3 DS3sSTS-12, OC-12622.080Mb/s336 DS1s or 12 DS3sSTS-48, OC-482488.320Mb/s1344 DS1s or 48 DS3sSTS-192, OC-1929953.280Mb/s5376 DS1s or 192 DS3sSTS-768, OC-76839813.12Mb/s21504 DS1s or 768 DS3s
Thus, each SONET STS-N electrical signal has a corresponding OC-N optical signal. The OC-N signals are created by converting the STS-N electrical signal to an optical signal. The SONET standard establishes a multiplexing format for using any number of 51.84 Mbps signals as building blocks. For example, an OC-3 (Optical Carrier, Level 3) is a 155.52 Mbps signal (i.e., 3 times 51.84 Mbps), and its electrical signal counterpart is referred to as an STS-3 signal. The STS-1 signal carries a DS3 signal or a number of DS1 or other lower level signals. A SONET STS-3 signal is created by concatenating STS-1 signals.
Telecommunication equipment at central offices (COs), remote terminals (RTs), wireless communication cell sites and other equipment locations is frequently deployed as one or more bays with multiple shelves, wherein each shelf is configured to receive a plurality of communications cards. A backplane is provided in each bay for communication between its cards and shelves, as well as for interbay communication. One of the more common types of equipment to be found at these equipment sites is SONET multiplex equipment which takes lower-rate (tributary) signals, such as DS1 (1.5 Mbps), DS3 (45 Mbps), OC-1 (51.84 Mbps), or OC-3 (155.52 Mbps), and time division multiplexes them into a higher-rate signal such as OC-3 or OC-12 (622.08 Mbps). The SONET multiplex equipment also performs the corresponding demultiplex function of recovering the lower rate tributary signals from an incoming higher-rate signal.
Telecommunications companies are eager to provide as much performance as possible from their existing infrastructure. Their telecommunications systems are primarily based on the DS1 electrical signal hierarchy that uses DS0 data. A DS1 signal is comprised of 24 multiplexed DS0 voice channels. To provide capacity that meets the afore-mentioned demand for more bandwidth and high bit rates, telecommunications companies need equipment that is based on a higher data rate such as DS3 in which DS1 signals are the base signal for data channel multiplexing, as opposed to DS0 signals.
Problems with existing equipment managing DS3 traffic, however, are numerous. For example, DS3 hierarchy-based equipment requires more bay and shelf space in CO, RT, cell sites and other locations where equipment space is already a limited commodity, where bays and shelves are already crowded (e.g., many shelf card slots are filled with a card), and where room to add equipment with new features is very limited or essentially nonexistent.
In addition, previous generations of SONET and asynchronous multiplex equipment have dedicated fixed portions of an equipment shelf to different types/rates of services. For example, separate portions of the shelf are typically reserved for DS1, DS3, and OC3 interface units. Dedicating specific portions of the shelf to specific service types reduces the flexibility of the shelf, and typically leaves wasted shelf space for any given application.
Also, access to the optical connectors on existing multiplexer cards is typically on the front of a card, while access to the electrical connectors is on the back of the shelf. In equipment locations were space is limited, it can be difficult for human operators to gain access to the backs of card slots in a shelf of an equipment bay. A need therefore exists for SONET multiplexer equipment having a reduced form factor, with non-dedicated card slots, and with front panel access to both electrical connectors and optical connectors or, if the system includes high speed optical connections such as OC48 and lower speed optical connections such as Gigabit Ethernet, access to all of these connections on the front panel.
In the above co-pending applications, a SONET multiplexer is provided to perform OC3 to DS3 multiplexing and demultiplexing operations using a substantially reduced form factor as compared with existing SONET equipment that can perform the same multiplexing functions. The SONET multiplexer is implemented as a single card (i.e., capable of deployment on a single card slot in a telecommunications bay equipment shelf). The SONET multiplexer comprises a face plate and two attached circuit boards and referred to as the main board and the lower board. The main board comprises a field programmable gate array (FPGA), the operations of which are described in the above-referenced co-pending applications. Thus, the SONET multiplexer is considerably smaller than existing SONET multiplexers having the same functionality, which consist of multiple plug-in cards. While single-card media converters are available to perform optical and electrical signal conversions, they are not able to sufficiently conform to the GR-499 and GR-253 standards to permit interoperability of equipment and signals at a basic level, such as the ability to transport a DS3 signal from one OC3 system to a different OC3 system over fiber optic cable as does the SONET multiplexer as described in the above co-pending applications.
The reduced form factor of the SONET multiplexer therefore overcomes many of the disadvantages of existing multi-card SONET multiplexers since it does not require much equipment space. Further, the SONET multiplexer can be deployed as a standalone component and therefore need not be inserted into a bay shelf at all, but instead can be mounted on the side of a bay, on a wall in the equipment area of the CO, RT or other user, on a top of a computer, table or other work surface, among other places.
The SONET multiplexer of the above listed co-pending applications allows front panel access to three DS3 ports, as well as an OC3 port. The single card implementation of the SONET multiplexer facilitates its use with other cards such as a wave division multiplexer (WDM) and a DS3 to DS1 multiplexer, which are described in the afore-mentioned application Ser. Nos. 10/448,453 and 10/448,463. By way of an example, the O3-3D3 MUX can be used within a high rise building receiving an OC-12 feeder. The O3-3D3 MUX can be used to drop DS3s to different floors. The DS3 to DS1 multiplexer can also be used to drop DS1s to different floors. The configuration of the O3-3D3, the DS3 to DS1 multiplexer and the WDM as single-card building components allows different arrangements of these cards in a small profile chassis or enclosure that is independent of equipment shelves for flexible installations, as described in the afore-mentioned application Ser. Nos. 10/448,453 and 10/448,463. Further, unlike existing SONET equipment, the chassis does not have dedicated card slots as described in more detail below in connection with FIGS. 7B through 7F.
Although compact and flexible configurations of SONET multiplexing and transport devices for DS3 service, as described in co-pending applications, are available, a problem continues to exist with respect to providing power to these devices. Local alternating current (AC) power is required for powering such equipment located at a business' premises even though powering of lower speed (DS0 and or DS1) services is customarily done from communications service provider's Central Offices, Remote Terminals or other provider's locations distant from the business' premises. Due to the increased demand for high speed data networking capabilities, the additional expense of providing local power for the communication is justified. Furthermore, if the business is dependent upon the continuous availability of the high speed networking capability, then the cost of back-up power systems may also be justified. These back-up systems may comprise emergency generators, batteries or similar business-premises-located equipment designed to provide emergency power.
Generators are expensive and usually only large facilities use these. Often times, businesses in large, urban office buildings do not have the luxury of being able to place a large generator outside or on top of the office building. Additionally, if the business is spaced over multiple floors or even adjacent buildings, running power cable between floors or buildings is prohibitively expensive.
Batteries are another solution that is not entirely feasible because of maintenance and storage locations required by the batteries. In addition, the batteries may comprise harmful chemicals that either have special ventilation or handling requirements. Therefore, businesses expend large sums of money to provide reliable power to their telephonic communication devices.
Local emergency power arrangements are inefficient, more expensive to operate and less reliable than the much larger battery and generator arrangements presently in use by telecommunication service providers.
Span power is used to power some communication devices such as telephones that provide plain old telephone service (POTS) or devices used to provide a business customer interface to DS1 service (also known as T1 service). Span power is supplied to the communication equipment on communication wires that are separate and distinct from the wires of the local electrical utility and, further, span power wires may be separate from the wires used to carry services. Typically, the equipment of today, although it requires less power than older equipment, requires more power than what the typical span powering arrangement can provide. An example of prior art span powering is shown in U.S. Pat. No. 6,580,254 B2 issued to Schofield.
A further problem of span power approaches is that the maximum distance between two given nodes is limited by the DC voltage drop on the span power lines. Therefore, conventional high speed communication equipment (such as that providing DS3 or higher speed services) in combination with the DC voltage drop has made span powering of such devices unfeasible.
There is a need for a span powering solution that supports full DS3 or higher speed services as required by the end user without being cost prohibitive due to construction and equipment costs, or severely distance limited as a result of the DC voltage drop, while providing adequate power for the DS3 or higher speed services.